Ken HudnutUSGSPasadena, California

CSUN

Northridge, California

April 23, 2002

… … and some and some aspects of theaspects of the

1999 Hector Mine 1999 Hector Mine earthquakeearthquake

Merging geodesy and Merging geodesy and geology: SCIGN, laser geology: SCIGN, laser topographic mapping …topographic mapping …

The major objectives of theThe major objectives of theSCIGN array are:SCIGN array are:

• To provide regional coverage for estimating earthquake potential throughout Southern California

• To identify active blind thrust faults and test models of compressional tectonics in the Los Angeles region

• To measure local variations in strain rate that might reveal the mechanical properties of earthquake faults

• In the event of an earthquake, to measure permanent crustal deformation not detectable by seismographs, as well as the response of major faults to the regional change in strain

The SCIGN 250 station array was unveiled on July 6, 2001

“SCIGN data quality is excellent – probably the bestof any network in the world…” – Tom Herring, 6/19/01

Scientific Director, UNAVCO at the 2001 SCIGN Annual

Meeting

Plate Boundary Plate Boundary Observatory (PBO)Observatory (PBO)

New sites:•Backbone and clusters:

•Alaska and Cascadia•Volcanic complexes•San Andreas fault zone

Existing sites:•PANGA, BARD, EBRY, BARGEN, LVC, SCIGN

PBO San PBO San

Andreas planAndreas plan

New sites:•Clusters along San Andreas fault, especially along transitions from creeping to locked sections

Existing sites:•BARD, SCIGN, LVC,and BARGEN

High resolution topography along surface rupture of the High resolution topography along surface rupture of the October 16, 1999 Hector Mine, California Earthquake October 16, 1999 Hector Mine, California Earthquake

(M(Mww7.1) from Airborne Laser Swath Mapping7.1) from Airborne Laser Swath Mapping

HUDNUT, K. W., U. S. Geological Survey BORSA, A., IGPP/SIO, UCSDGLENNIE, C., Aerotec LLC

MINSTER, J.-B., IGPP/SIO, UCSD

In press, Bulletin of the Seismological Society of AmericaSpecial Issue on the Hector Mine earthquake (2002)

http://pasadena.wr.usgs.gov/office/hudnut/BSSA_ALSM/

ALSM, InSAR and TM imagingALSM, InSAR and TM imagingand mapping before & afterand mapping before & after

Laser scan of landsurfaces and urbaninfrastructure – buildings & lifelines- damage assessment

Pre- and post-disaster images can be differenced to measure damage and track recovery

LANDSAT 7 – earthquake damage - Bhuj, India

ALSM – 9/11/01

NYC

Active Faults in Southern CaliforniaActive Faults in Southern California

Surface RuptureSurface Rupture

Previously mapped, but un-named

Lavic Lake fault in recognition of breaks through dry lake bed

Up to 5.25 meters of right-lateral motion

48 km overall length of surface rupture

Only ruptured once prior through ~50 ka alluvium

Hector Mine (MHector Mine (Mww7.1)7.1)

Photo by Paul ‘Kip’ Otis-Diehl,USMC, 29 Palms

ALSM (Scanning LIDAR imaging)ALSM (Scanning LIDAR imaging)

Slow, precise helicopter flight line data acquisition at 200-300 m AGL.

6888 pps near infra-red (1064 nm) laser.

Scan Width: +/- 20 degrees. Nominally, 180 meters full-width.

200 pulses across swath, ~ 80cm spacing.

Footprint Diameter: Nominally 40cm. Half-meter posting, 15cm horizontal one-sigma

absolute accuracy specified.

Integrated GPS & INS navigation and attitude determination.

Pitch Mirror Correction: maximum +3.5/-6.5 degrees (+ forward bias).

R r

v

Geolocation Vectors and Error Sources

r

Vector from CMearth to GPS phase centerMagnitude & directional errors both arestochastic, time and location variant.

R

vVector from GPS phase center to laserMagnitude error is constant if no airframe flexing. Directional error due to constant and time-varying biases in INS.

Vector from laser to ground footprintMagnitude error due to timing, instrument and atmospheric delays. Directional errorfrom constant mirror mounting offsets and time-varying biases in reporting of scanangles (both pitch and roll).

Note: additional errors due to imperfectsynchronization of GPS, INS, mirror scanand laser firing times must be modeled and removed as well.

Flight PlanFlight Plan

Two overlapping swaths

200-500m mapped width

70 km long

GPS network ≥ 1 Hz

Temporary GPS stations

Cross-swath spurs Roll/Pitch/Yaw calibration maneuvers over dry lake

Flights over well-mapped Hector Mine

GPS Sites at ≥1Hz During ALSM Mission

1Hz 2Hz

BMHLOPBLOPCPRDMTSIBETROY

AGMTHCMNNBPSOPCLOPCXOPRD

Calibration maneuvers at

Hector Mine and Lavic Lake

Fly-through the along faultFly-through the along fault

Hector Mine Mobile GPS Survey Sites

Southwest Corner of Lavic Lakedry lake bed for calibrations

Helicopter videos:Helicopter videos:45 & 90 degree angles45 & 90 degree angles

New methods to explore, new synergies New methods to explore, new synergies between data types (e.g., GPS & ALSM)between data types (e.g., GPS & ALSM)

Combinations of seismic, geologic, and geodetic data in new ways– Source modelling– Hazard modelling

Cross-overs between fields– Geology and

geodesy with InSAR and ALSM

– Seismology and geodesy with high-rate GPS

1999Hector Mineearthquakesurfacerupture

ALSM-Derived Contours of Bullion Mountain Segment

(blue lines are1-foot contours)

Lidar (Bullion Fault)… ContoursLidar (Bullion Fault)… Contours

Lidar…. Raw SpotsLidar…. Raw Spots

To assess geodetic capability of To assess geodetic capability of repeat-pass ALSM:repeat-pass ALSM:

calibration requirementscalibration requirementsGeometry: mount angles, scan offsets, GPS-Laser

vector, GPS antenna phase center.Delays: electronic, optical, atmospheric.Reference point on laser platform.Timing of various components: e.g. INS vs. GPS

vs. mirror attitude sensors.Stabilization platforms (delays, accuracy).Detectors (thresholds, amplitude-range “walk”).

Lavic LakeRoll & PitchManeuvers

Explodedordnance(crater)

pitch maneuvers

15 cm vert.

10 cm vert.

Ramp probably due to roll or scan bias

End biases are real (low roll/ pitch section)

Excellent shot- to-shot varia-bility (5cm rms)

Cal/Val Maneuver StacksCal/Val Maneuver Stacks

Geological quantification and Geological quantification and questionsquestions

Tectonic interpretation of strain release in great earthquakes from their surface rupture– Basic documentation of surface rupture

e.g., Kurushin et al. (1997) study of 1957 Gobi-Altay eq.

How does slip vary along-strike?– e.g., need to assess variance and error in slip rate estimates from

paleoseismic methods e.g., Barka et al. (2002) and Rockwell et al. (2002) extensive studies of

1999 eq.’s in Turkey and similar studies of Hector Mine earthquake (in press, BSSA)

– is high-frequency energy radiated from fault?

Does slip vary from one earthquake to the next?– can detailed topographic mapping of geomorphic features along the

fault be modeled by repeats of exactly the same slip in successive earthquakes, or must slip vary in order to explain the topography?

– slip variation models for earthquake recurrence strongly influence seismic hazard analyses – assumptions made in these analyses necessarily simplify faulting processes, with societal repurcussions

Lavic Lake – compressional stepLavic Lake – compressional step

Oblique view Oblique view and photo of and photo of thrust wedgethrust wedge

Estimating slip Estimating slip on ‘max. slip’ on ‘max. slip’ segment ofsegment of

the faultthe fault

Estimating slip on Estimating slip on ‘max. slip’ segment of‘max. slip’ segment of

the faultthe fault

Conclusions - and some open questionsConclusions - and some open questions Airborne LIDAR imaging (ALSM) offers remarkable promise for

geomorphology, even over inaccessible or vegetated areas Commercial operations are reliable and affordable on well-specified

targets with carefully designed deployments (same as photogrammetry) CAL-VAL maneuvers are essential for geodetic-quality mapping of

geomorphological features Turning ALSM into a geodetic-quality tool requires careful calibration and

considerable analysis

Slip estimation:– has been initially developed demonstrated– new and improved methods are being developed– systematic measurement along the surface rupture will be done and then

compared with geologic estimates, InSAR and other methods– quantitative assessment of slip variation along-strike

dynamic faulting models – is high-frequency energy radiating from the fault?

Quantitative geomorphology– Model tectonic landform evolution

Did topographic features form as a result of exactly repeated slip distributions? Can topography be explained by only certain combinations of slip in past events?